The purpose of this project is to study the physical, chemical, and ultrastructural properties of calcium phosphate salts, and to clarify the kinetic and thermodynamic processes and the interactions with substances of biological interest that uniquely enable calcium phosphate salts to carry out their specialized role in vivo. The properties of calcium phosphate salts are being studied with a variety of ultrastructural and physical-chemical techniques such as electron microscopy, x-ray diffraction, surface area analyses, chromatographic and standard analytical chemistry procedures. The principal endeavor currently being pursued involves artificial lipid vesicles (liposomes) as in vitro models to investigate physico-chemical aspects of matrix vesicle (MV)-mediated calcification in vivo. The latest phase of this endeavor, a study that examined the modulating effect of cartilage matrix proteoglycans (aggrecan) on mineral development in the liposomal model system, was completed during the report period. Findings from this study showed that enzymatic breakdown of extraliposomal proteoglycans (PG) does not necessarily destroy the retarding effect PGs have on calcium phosphate precipitation in liposomal suspensions. Core protein as well as glycosaminoglycan components, but not hyaluronic acid, are equally as effective as intact PG in delaying precipitate development. On the other hand, the breakdown products of chondroitinase digestion of the glycosaminoglycan components and of proteinase digestion of the core protein do not have a strong inhibitory effect on the precipitation. These data suggest that the core protein and glycosaminoglycan chains may have to be destroyed before PG, when freely suspended in solution, loses its inhibitory influence on biomineral development.